This invention relates to an actuator, with magnetic attraction and locking, comprising an energising winding, and a movable core having a first portion which passes axially into the winding, a second portion and a third portion both external of the winding, and a magnetic field structure an element of which enters partially into the winding to present a first polar surface cooperating by an axial gap with the first portion, other elements of this magnetic field structure extending about the winding in order to form a second polar surface cooperating by a second radial gap with the second portion of the core, and to form a third polar surface cooperating with the third portion of the core by a third axial gap which is both small and precise.